Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.44	4.607%	$92.5144	$92.51	$92.50	$92.50
Purchase #2	$144.73	9.355%	$158.2695	$158.27	$158.25	$158.30
Purchase #3	$148.62	6.192%	$157.8226	$157.82	$157.80	$157.80
Purchase #4	$230.44	4.358%	$240.4826	$240.48	$240.50	$240.50
Purchase #5	$77.79	7.213%	$83.401	$83.40	$83.40	$83.40
Purchase #6	$47.64	10.250%	$52.5231	$52.52	$52.50	$52.50
Purchase #7	$177.83	4.408%	$185.6687	$185.67	$185.65	$185.70
7 purchase totals =	$915.49		$970.6819	$970.67	$970.60	$970.70